It is well known that fused silica quartz has exceptional elastic characteristics that make it capable of being the basis for high accuracy pressure sensors. Its well known limitations, however, are fragility and low effective tensile strength. This becomes particularly critical in designing diaphragm operated high pressure capacitor sensors since any usable deflection of a diaphragm is also accompanied by stress levels in the diaphragm which can cause failure in the diaphragm material. The stress occurs when a diaphragm bends and develops compression and tensile forces in the quartz.
Another problem in constructing fused silica pressure sensors is bonding of quartz members to one another. Glass frits are generally used for this purpose but they have inferior properties relative to the properties of quartz silica. Glass frits also introduce temperature dependent stresses in the quartz because their expansion characteristics are significantly different from the extremely low values exhibited by fused silica quartz. Additionally, the glasses that are most suitable for bonding fused silica fire at very high temperatures (900 degrees Centigrade) and where metal films are utilized there is a great likelihood that extreme degradation of metal films used in the construction will occur.
It is an object of this invention to circumvent all of these limitations and create a low cost, high pressure, fused silica capacitance pressure sensor. The design also lends itself to low pressure sensor fabrication.